In many optical systems, it is often useful to separate and/or combine light beams having different optical characteristics, e.g., polarization states, wavelengths, etc. For example, in optical data storage systems, the optical qualities of the storage medium are altered in a manner such that changes in the reflective or transmissive properties of the medium are representative of the information recorded thereon. This information is commonly transmitted to and retrieved from the optical medium using light beams produced by a laser light source.
The information recorded on the disc is retrieved from the disc by directing a laser beam onto the disc. The reflected laser beam is then directed onto the detecting surface of a photodiode or other light detector system which transforms the reflected or transmitted laser beam signal into an electrical signal. In this manner, the data stored on the disc is transferred from the disc to the laser beam and converted into an electrical signal which carries the same information recorded on the disc. This electrical signal is further processed, and ultimately results in retrieval of the computer data, audio sound, video images, etc., represented by the information recorded on the disc.
Various devices have been produced for accomplishing the optical data storage procedures. Such previous devices for reading and/or writing data on optical discs typically comprise a number of discrete components for processing the light beam emitted from the laser diode. For example, such devices may include a full cube beamsplitter which is used in combination with a separate, detached collimator lens, an objective lens, a detached light source, and an array of detector elements. In particular, devices such as those illustrated in U.S. Pat. Nos. 4,399,529 and 4,507,766 illustrate the extensive number of components in some prior devices for achieving the desired result.
These prior devices experience a number of problems in connection with their operation. In particular, because of the large number of components required in these devices, they become bulky and are difficult to incorporate into a head configuration which can be easily utilized in an optical system for recording and reading data carriers. Furthermore, the large number of components creates difficulties in obtaining and maintaining element alignment and focus of the beams transmitted therethrough. In addition, the combinations of these various components create various losses in the optical efficiency of the device due to light which is lost as the beams propagate through the various device components.
Some previous devices have been based upon diffractive or holographic elements and an integrated laser diode and servo signal detector diode package. Such a system is disclosed, for example, in U.S. Pat. No. 4,624,526, wherein a diffraction grating or hologram lens is used instead of a prism for directing a read-out light beam emitted by a light source to the surface of a recording medium. However, this type of system also experiences losses in optical efficiency as the light is scattered and lost during transmission through the components of the device.